Production of pure metals



' Patented-June 28, 1932 UNITEDSTATES PATENT OFFICE LEO SCHLECHT, OF LUDWIGSHAFEN-ON-THE-RHINE, AND FRANZ DUFTSGHMID, OF

HEIDELBERG, GERMANY, ASSIGNORS TO I. G. FARBENINDUSTBIE AKTIENGESELL- SCHAFT, OF FRAN-KFORT-ON-THE-MAIN, GERMANY, A. CORPORATION OF GERMANY rnonuorron or roan METALS No Drawing. Application fi-led August 12, 1929, Serial No. 385,473, and in Germany August 27, 1928.

The present invention relates to the production of pure metals by the removal from metal powders of the impurities which form volatile compounds with oxygen.

It is already known that the purification of metal powders which contain constituents which form volatile compounds with oxygen, such as carbon, sulphur and the like in a free, combined, or dissolved state, can be carried out by adding oxides to the metal powder and heating. The economy of this process especially depends on the duration of the heat treatment, that is to say on the velocity of formation of the volatile oxygen compounds of the impurities concerned.

We have now found that the purification process can be considerably shortened by first subjecting the metal powder to be purified to a uniform oxidizing treatment and then volatilizing the impurities from the product obtained, by heating. By the oxidizing pre treatment a uniform distribution of the combined oxygen such as can only be obtained with difliculty, if at all, by mechanically mixing oxides with the metal powder, is

easily obtained.

The oxidation of the metal powder is preferably carried on only until the oxygen content is just sufficient for the formation of the volatile oxygen compounds of the impuri such as for instance oxygen, air, carbon dioxide, water in the liquid or vaporous state and the like, and in'some cases even at ordinary or only slightly elevated temperatures. The volatilization of the impurities proceeds with a sufiicient velocity even at about 500 eentigrade. It is preferably carried out by heating the metal powder, which has been subjected to"'a previous oxidizing treatment, in an inert or reducing gas, preferably flow ing, and if desired with increased or decreased pressure.

In many cases the manufacture of the metal powder, the oxidizing treatment and sometimes also the volatilization of the impurities canbe carried out in one operation. Thus, for instance, iron powder containing oxygen besides carbon may be produced by decomposing iron carbonyl in the hot free space of a heated vessel while introducing into the vessel a calculated amount of an oxidizing gas, such asfor example air. By a consecutive heat treatment of the uniformly oxidized iron powder an iron powder free from carbon can immediately be obtained. The said heat treatment for eliminating the carbon and oxygen content may also be combined with the production of the iron powder and the oxidizing treatment thereof by allowing the iron powder produced and sufficiently oxidized in the aforesaid mannerto fall through a tube heated to between 800 and 1000 C., or into a melt of iron in case it be intended to produce compact 'iron free I from carbon.

The purified metal powders are particular- 1y suitable for the production of moulded metal articles. For this purpose the volatilization of the impurities from the pretreated metal powder can be carried out at so high a temperature, if desired with thesimultaneous or subsequent employment of pressure,

"I -that the consolidation of the metal powder toporous or nonporous metal articles occurs.

In consequence of the uniform distribution vention is not restricted to these examples.

li'wample 1 Iron powder containing 1.12 per cent of C, prepared by the thermal decomposition of iron carbonyl, is moistened with waterand dried at 100 centigrade, and in this manner. each single particle of iron becomes coated with a blue black film of oxide. This not been pretreated but which has been intimately mixed with the necessary quantity of iron oxide takes three times as long at the same temperature.

. Example 2 Iron powder containing carbon is super- .ficially oxidized in the manner indicated in Example 1. The resulting powder is filled into a crucible and heated to about 1200 C. in a glowing furnace. The carbon is removed with the disengagement of carbon monoxide. Thereby further oxidation of the iron due to the action of the atmosphere within the furnace is avoided. Simultaneously the iron powder sinters, and an iron block free from carbon is obtained, which can be further treated by rolling.

What we claim is:

1. The process of producing pure metals which comprises subjecting powdery metal containing impurities which form volatile oxygen compounds, to a uniform oxidizng treatment at a temperature sufliciently low to uniformly superficially oxidize the metal and to avoid any substantial formation of volatile compounds, and then heating the resulting product, thereby causing the impurities to react with the mtroduced oxygen to form gaseous products.

2. The process of producing pure metals which comprises subjecting powdery metal containing impurities which form volatile oxygen compounds, to a uniform oxidizing treatment at a temperature sufiiciently low to uniformly superficially oxidize the metal and to avoid any substantial formation of volatile compounds, and then heating the resulting products to sintering temperature,

thereby causing the impurities to react with the introduced oxygen to form gaseous prodnets.

3. The process of producing pure metals which comprises sub ecting powdery metal containing impurities which form volatile oxygen compounds, to a uniform oxidizing treatment to uniformly superficially oxidize the metal to only such an extent as is sufficient to produce volatile oxygen compounds of the impurities to be removed,'at a temperature sufficiently low to avoid any substantial formation of volatile compounds, and then heating the resulting products, thereby causing the impurities to react with the introduced. oxygen to form gaseous products.

4. The process of producing pure metals which comprises subjecting powdery metal containing impurities which form volatile oxygen compounds, to a uniform oxidizing treatment to uniformly superficially oxidize the metal to only such an extent as is sufiicient to produce volatile oxygen compounds of the impurities to be removed, at a temperature sufliciently low to avoid any substantial formation of volatile compounds, and then heating the resulting product to sintering temperature, thereby causing the impurities to react with the introduced oxygen to form gaseous products.

5. The process of purifying iron powder which comprises subjecting said powder to an oxidizing treatment, at a temperature not substantially exceeding 100 (1., until said powder uniformly takes up an amount of oxygen sufiicient to combine with the impurities in the iron to form volatile compounds thereof and then heating the resulting prod not to a temperature above 500 C. to drive the volatile compounds of said impurities our hands.

LEO SOHLECHT. FRANZ DUFTSCHMID. 

